(Electronegativity, Valence Electrons) Tuesday November 9, 2010 (Electronegativity, Valence Electrons)

Bell Ringer Tuesday, 11-9-10 Which one of the listed elements has the largest atomic radius – K, Co, Br the least ionization energy – Na, P, Cl the greatest electron affinity – Li, B, F the greatest ionization energy – Li, K, Fr

Announcements This is the last week of the 2nd six- weeks. Be sure to check you grades and see me if you want to improve upon your score.

Assignment Currently Open Date of Notes on Website Page Date of Notes on Website Date Issued Date Due WS: Atomic Structure 73-74 10/1 10/8

Electronegativity The outer-most, highest energy level electrons in an atom’s electron cloud are called its “valence” electrons. Valence electrons are the ones that participate in chemical bonding – the force that hold elements together to form compounds. When two atoms are bonded together, one of the atoms may “tug” harder at the participating valence electrons harder than the other atom does. Electronegativity is a measure of the ability of an atom in a chemical compound to attract electrons. are inter

Electronegativity Electronegativity values tend to increase across each period, although there are exceptions. increase are inter

Electronegativity Electronegativity values tend to either decrease down a group or remain about the same. Decrease/remain same are inter

least electronegative Electronegativity The alkali and alkaline-earth metals are the least electronegative elements. In compounds, their atoms have a low attraction for electrons. least electronegative are inter

Electronegativity Nitrogen, oxygen, and the halogens are the most electronegative elements. Their atoms attract electrons strongly in compounds. most electronegative are inter

Electronegativity The Noble gases are unusual in that some of them do not form compounds and therefore cannot be assigned electronegativity values. But when a Noble gas does form a compound, its electronegativity is rather high, similar to the values for the halogens. are inter

Electronegativity The combination of the period and group trends in electronegativity results in the highest values belonging to the elements in the upper right of the periodic table. The lowest values belong to the elements in the lower left of the table. highest lowest are inter

Electronegativity The alkali metals cesium and francium have the lowest electronegativity values at 0.7. The halogen fluorine has the highest electronegativy value at 4.0. highest are inter lowest

Valence Electrons electrical neutrality and, chemical stability Two very important conditions for atoms are: electrical neutrality and, chemical stability All atoms that have equal numbers of protons and electrons are electrically neutral. However, only the Noble gases are also stable. All other atoms bond to form chemical compounds because that’s the way to become stable.

Valence Electrons In the process of bonding, atoms either lose, gain, or share their valence electrons. Remember that these valence electrons are those in the atoms’ outermost, highest energy level, and as a result are the ones most subject to the influence of other nearby atoms or ions.

Valence Electrons In this chemistry class, we will deal primarily with valence electrons located in an atom’s highest energy level s and p sub-levels. For example, the element sodium has an electron configuration notation of 1s2, 2s2, 2p6, 3s1 As you can see, sodium has only one electron in its highest energy level (3), and it’s in the s sub-level. This is the only electron sodium will use to bond. Another example: the element chlorine has an electron configuration notation of 1s2, 2s2, 2p6, 3s2, 3p5 Chlorine has 7 electrons in its highest energy level (3), 2 in the s sub-level and 5 more in the p sub-level. Chlorine counts all 7 of these valence electrons in its bonding considerations.

Valence Electrons For main block (s and p) elements, the valence electrons are the electrons in the outermost s and p sublevels. The inner electrons are in filled energy levels and are held too tightly by the nucleus to be involved in compound formation.

Valence Electrons The alkali metals of group 1 have 1 valence electron. The alkaline earth metals of group 2 have 2 valence electrons. The elements in the p block (groups 13–18) have a number of valence electrons equal to their group number minus 10. For example, group 13 has 3 valence electrons, group 14 has 4, etc. In some cases, both the s and p sublevel valence electrons of the p-block elements are involved in compound formation. In other cases, only the electrons from the p sublevel are involved.